1. Field of the Invention
The present invention relates in general to a closed circuit television (CCTV) monitoring system, and more particularly to a bidirectional communication system for a CCTV which is useful to bidirectional communication in a CCTV monitoring system.
2. Description of the Prior Art
Referring to FIG. 1A, there is shown a block diagram of a conventional CCTV monitoring system. As shown in this drawing, the conventional CCTV monitoring system comprises a plurality of cameras CAM1-CAM4 installed in places to be monitored, a video selector 1 for selecting desired one of video signals from the plurality of cameras CAM1-CAM4 , and a monitor 2 for displaying the video signal selected by the video selector 1.
The operation of the conventional CCTV monitoring system will hereinafter be described.
The plurality of cameras CAM1-CAM4 installed in the places to be monitored shoot objects in the monitored places and output the resultant video signals. A desired one of the video signals outputted from the plurality of cameras CAM1-CAM4 is manually or automatically selected by the video selector 1. The video signal selected by the video selector 1 is displayed through the monitor 2.
Therefore, an observer can monitor the plurality of places shot by the plurality of cameras CAM1-CAM4 through the single monitor 2.
Referring to FIG. 1B, there is shown a block diagram of a voice output system which is applied to the conventional CCTV monitoring system. The voice output system in FIG. 1B is provided in the conventional CCTV monitoring system such that the observer issues an order or sends a message while watching a video picture shot by the camera. The voice output system comprises a microphone MIC for converting a voice from the observer into an electrical voice signal, a voice output circuit 3 for amplifying the voice signal through the microphone MIC by a predetermined level and outputting the amplified voice signal, and a plurality of speakers SP1-SPn for converting the electrical voice signal outputted from the voice output circuit 3 into the original voice.
The observer while watching the monitor 2 outputs the voice signal through the microphone MIC to the places being shot by the cameras CAM1-CAM4. The voice signal through the microphone MIC is amplified by the predetermined level and then fed to the speakers SP1-SPn by the voice output circuit 3. As a result, the observer can send a message to the places being shot by the cameras.
However, the conventional CCTV monitoring system has a disadvantage, in that the voice output system is further provided to send the voice message from the observer to the places being monitored, resulting in an increase in the cost. Also, the observer confirms the video picture of the place being monitored with the eye through the monitor and sends the voice message to an object in the place utilizing the voice output system and the voice from the observer is sent through the plurality of speakers. As a result, there may be wanting in an accuracy of the communication. Furthermore, a smooth monitoring network cannot be built up since the object in the place being monitored has no means for communication with the observer.